EP0210805B1 - Cathode for electron tube - Google Patents

Cathode for electron tube Download PDF

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Publication number
EP0210805B1
EP0210805B1 EP86305560A EP86305560A EP0210805B1 EP 0210805 B1 EP0210805 B1 EP 0210805B1 EP 86305560 A EP86305560 A EP 86305560A EP 86305560 A EP86305560 A EP 86305560A EP 0210805 B1 EP0210805 B1 EP 0210805B1
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EP
European Patent Office
Prior art keywords
earth metal
oxide
rare earth
coating
cathode
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP86305560A
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German (de)
English (en)
French (fr)
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EP0210805A3 (en
EP0210805A2 (en
Inventor
Masato C/O Mitsubishi Denki K.K. Saito
Keiji C/O Mitsubishi Denki K.K. Fukuyama
Masako C/O Mitsubishi Denki K.K. Ishida
Keiji C/O Mitsubishi Denki K.K. Watanabe
Toyokazu C/O Mitsubishi Denki K.K. Kamata
Kinjiro C/O Mitsubishi Denki K.K. Sano
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Priority claimed from JP60160851A external-priority patent/JPS6222347A/ja
Priority claimed from JP22930385A external-priority patent/JPH0626096B2/ja
Priority claimed from JP60229304A external-priority patent/JPS6288239A/ja
Priority claimed from JP60229302A external-priority patent/JPS6288240A/ja
Priority claimed from JP23190485A external-priority patent/JPH0782804B2/ja
Priority claimed from JP23190585A external-priority patent/JPH0743995B2/ja
Priority claimed from JP60231906A external-priority patent/JPS6290821A/ja
Priority claimed from JP61008365A external-priority patent/JPS62165832A/ja
Priority claimed from JP61008366A external-priority patent/JPS62165833A/ja
Priority claimed from JP61035670A external-priority patent/JPS62193031A/ja
Priority claimed from JP61035671A external-priority patent/JPS62193032A/ja
Priority claimed from JP4105086A external-priority patent/JPH0782800B2/ja
Application filed by Mitsubishi Electric Corp filed Critical Mitsubishi Electric Corp
Publication of EP0210805A2 publication Critical patent/EP0210805A2/en
Publication of EP0210805A3 publication Critical patent/EP0210805A3/en
Publication of EP0210805B1 publication Critical patent/EP0210805B1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/14—Solid thermionic cathodes characterised by the material
    • H01J1/142—Solid thermionic cathodes characterised by the material with alkaline-earth metal oxides, or such oxides used in conjunction with reducing agents, as an emissive material

Definitions

  • This invention relates to a cathode for an electron tube such as a cathode-ray tube of a TV set and particularly to an improvement in electron emission characteristics of the cathode.
  • Fig. 1 is a schematic sectional view illustrating a structure of a cathode for use in a cathode-ray tube (CRT) or an image pickup tube for a TV system.
  • a layer 2 of an electron-emissive substance made of an alkaline earth metal oxide containing at least BaO and further containing SrO and/or CaO is formed on a cylindrical base 1 essentially composed of Ni and containing a small amount of a reducing agent such as Si or Mg.
  • a heater 3 is provided inside the base 1 and the electron-emissive layer 2 is heated by the heater 3 to emit thermal electrons.
  • Such a conventional cathode is manufactured by a process as described below.
  • a suspension of a carbonate of an alkaline earth metal (Ba, Sr, Ca, etc.) is sprayed on the base 1 and the applied suspension is heated by the heater 3 in a dynamic vacuum.
  • the alkaline earth metal carbonate is converted to an oxide.
  • the alkaline earth metal oxide is partially reduced at a high temperature of 900 to 1000°C so that it is activated to have a semiconductive property, whereby an electron-emissive layer 2 made of an alkaline earth metal oxide is formed on the base 1.
  • a reducing element such as Si or Mg contained in the base 1 diffuses to move toward the interface between the alkaline earth metal oxide layer and the base 1, and then reacts with the alkaline earth metal oxide.
  • the alkaline earth metal oxide is barium oxide (BaO)
  • the reaction is expressed by the following formula (1) or (2).
  • BaO + 1/2Si Ba + 1/2SiO2
  • BaO + Mg Ba + MgO (2)
  • the alkaline earth metal oxide layer 2 formed on the base 1 is partially reduced to become a semiconductor of an oxygen vacancy type. Consequently, an emission current of 0.5 to 0.8 A/cm2 is obtained under the normal condition at an operation temperature of 700 to 800°C.
  • an intermediate layer of an oxide or a composite oxide such as Si02, Mg0 or Ba0.Si02 is formed in the interface region between the base 1 and the alkaline earth metal layer 2 as is obvious from the formulas (1) and (2), so that the current is limited by a high resistance of the intermediate layer.
  • the intermediate layer serves to prevent the reducing element in the base 1 from diffusing into the electron-emissive layer 2 so that a sufficient amount of Ba may not be generated.
  • an oxide coated cathode for an electrode tube comprising: a metal base essentially composed of nickel and including either one or both silicon and magnesium reducing agents; and a coating of electron emissive alkaline earth metal oxide, which oxide is coated on said base, and is essentially composed of barium oxide; wherein said oxide-coated cathode is characterised by: incorporation of a rare earth metal additive, containing at least one of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, holmium, dysprosium, erbium or thulium, in said metal base, or said coating, or as an interlayer located between said metal base and said coating, as follows: as 0.01 to 0.5 wt.% rare earth metal in said base; or as 0.05 to 15 wt.% rare earth metal in said coating; or as 0.1 to 20 wt.% rare earth metal oxide in said coating
  • rare earth metal additives are particularly beneficial and affords a solution to the problem of oxide barrier formation.
  • the advantages of incorporating rare earth metal additives as aforesaid are many fold.
  • Rare earth metal additive when present in the electron emissive alkaline earth metal oxide coating contributes to the liberation of free barium. This alone contributes to an enhancement and maintenance of emission current.
  • the rare earth metal additive is active to inhibit or reduce the formation and accumulation of barrier oxide and thus enables diffusion of the reducing agent silicon and/or magnesium to be sustained during operation. Accordingly the emission current versus time characteristic of the oxide coated cathode is significantly improved and also it is better adapted for use at high current densities i.e.
  • EP-A-0204477 being a prior art according to Article 54(3) EPC for DE, FR and NL discloses an oxide coated cathode for an electron tube having a base essentially composed of nickel and including at least one of silicon and magnesium as a reducing agent.
  • the base is coated with a coating essentially composed of barium oxide but which also may include strontium and calcium alkaline earth metal oxide constituents.
  • a rare earth metal additive, scandium, is incorporated as 0.1 to 20 wt.% oxide in the coating and in use serves to reduce the rate of decrease in emission current occurring during the lifetime of the cathode.
  • German Patent Laying-Open DE-A-2626700 discloses an electron-emissive substance for high-pressure discharge lamp where an alkaline earth metal oxide such as BaO is mixed with an oxide of W or Mo and a rare earth metal oxide.
  • Patent DE-C-477232 discloses a cathode with a nickel wire to which is added a rare earth metal such as yttrium or scandium. It does not disclose the presence of an alkaline earth metal oxide (principally containing barium oxide) nor the presence of a reducing agent.
  • Patent US-A-1794298 discloses a cathode which is of the impregnated type rather than a coated oxide cathode. In its composition it has a base including nickel, but there is no teaching of the inclusion of a reducing agent.
  • This composition may include calcium, strontium or barium oxide (alkaline earth metal oxides) in the amount of e.g. 3% and a rare earth metal oxide of not more than 1% but exemplified as 0.003%.
  • a low proportion of rare earth metal oxide and the critical absence of a reducing agent do not permit the attainment of enhanced current density operation as afforded by cathodes according to embodiments hereinafter described.
  • German Patent Specification DE-C-880181 discloses the incorporation of the rare earth metals lanthanum or cerium in the nickel base of an oxide coated cathode. This is used in substitition for carbon in the production of passive nickel. Only sufficient amount of rare earth metal is added to reduce any nickel oxide that is formed during heat treatment of the nickel during processing.
  • German Patent Specification DE-C-976106 concerns the manufacture of cathode grade nickel. It discloses the addition of rare earth metal during processing and is directed to provide improvement in cold forming. It is said that reducing agent additives such as silicon should be avoided since these have a tendency during device operation to form an oxide barrier between the oxide coating and the nickel base.
  • Japanese Kokai JP-A-535011 discloses a pressed oxide cathode and not an oxide coated cathode as in the present invention.
  • the pressing is composed of nickel powder, alkaline earth metal oxides and reducing metals such as tungsten, molybdenum, tantalum, boron, aluminium, silicon, titanium, zirconium or manganese and rare earth metals such as cerium.
  • Japanese Kokai JP-A-59138033 discloses an oxide cathode structure in which the base metal contains zirconium or hafnium reducing agents. O.1 to 2 wt.% lanthanum or yttrium is added during manufacture as a controlling agent to prevent or reduce crystal grain growth such as might arise during high temperature processing.
  • a layer 2 of an electron-emissive substance formed on a base 1 comprises an alkaline earth metal oxide as a principal component containing at least BaO and additionally containing SrO and/or CaO in certain circumstances.
  • This layer 2 of the electron-emissive substance further contains a rare earth metal oxide of Sc or Y in 0.1 to 20 wt.%.
  • the above described cathode can be manufactured by the below described process.
  • scandium oxide powder or ytrium oxide powder is mixed in a ternary carbonate containing Ba, Sr and Ca, by an amount corresponding to a desired wt.% (to be obtained after the above stated ternary carbonate has been all converted to oxide).
  • nitrocellulose lacquer and butyl acetate are added to the mixture thus obtained so that a suspension is prepared.
  • This suspension is applied to the base 1 containing Ni as a major element by a spray method so that the applied suspension has a thickness of approximately 80 ⁇ m.
  • the carbonate is decomposed to oxide, in the same manner as in the prior art, and the oxide is partially reduced so that the electron-emissive layer 2 on the base 1 is activated.
  • cathodes provided with electron-emissive layers 2 containing Sc2O3 or Y2O3 in various wt.% were prepared. Then, diode vacuum tubes using those cathodes were prepared and they were subjected to life tests using various constant current densities so that changes in the emission current under the normal condition after the tests were examined. Fig.
  • FIG. 2A shows the emission current in a cathode containing Sc2O3 in 5 wt.%, a cathode containing Y2O3 in 12 wt.% and a conventional cathode not containing any rare earth metal oxide, respectively, after the life test using a constant current density (2.05 A/cm2) 3.1 times as large as the operation current density 0.66 A/cm2 of a conventional cathode for CRT under the normal condition.
  • the vertical axis in Fig. 2A represents the ratio of the emission current under the normal condition after the life test to the initial emission current under the normal condition.
  • an initial emission current of 1 to 2 A/cm2 can be obtained under the normal condition at the operation temperature of 700 to 800°C.
  • the cathodes containing rare earth metal oxides have characteristics that the emission current after the life test with the high current density is less lowered as compared with the conventional cathode.
  • Fig. 2B shows the ratio of the emission current under the normal condition after the life tests of 6000 hr to the initial emission current under the normal condition, as the result of the life tests conducted using a constant current density of 0.66 A/cm2 and constant current densities of twice, 3.1 times and 4 times that value with respect to the cathodes provided with electron-emissive layers 2 containing Sc2O3 or Y2O3 in various wt.%.
  • Sc2O3 or Y2O3 more than 0.1 wt.% has an effect in preventing lowering of the emission current under the normal condition after the life test with the high current density.
  • the content of a rare earth metal oxide in the electron-emissive layer 2 is preferably in the range from 0.1 to 20 wt.% and more preferably in the range from 0.3 to 15 wt.%.
  • Fig. 3A shows the results of the analysis in the interface region between the base 1 and the electron-emissive layer 2 of the conventional cathode.
  • the reducing agents Si and Mg are segregated in the vicinity of the interface between the base 1 containing Ni as a major element and the electron-emissive layer 2.
  • a peak of Si and that of Mg are observed at a position of approximately 5 ⁇ m from the interface toward the base 1 and at a position of approximately 3 to 5 ⁇ m from the interface toward the electron-emissive layer 2, respectively.
  • the largest peak of Si is observed at a position of approximately 13 ⁇ m from the interface toward the electron-emissive layer 2.
  • peaks of Ba were observed at the same positions as the peak positions of Mg and Si in the electron-emissive layer. Since these peak positions of Si, Mg and Ba are almost coincident to the peak positions of oxygen, these elements are considered to exist as oxides or composite oxides.
  • layers of SiO2, MgO and a composite oxide thereof are formed in the grain boundary in the base 1 near the interface during the life test with the high current density and layers of oxides BaO, MgO and SiO2 and composite oxides thereof are formed in the electron-emissive layer 2 at locations near the interface.
  • the layer of SiO2 ⁇ MgO and the layer of BaO ⁇ SiO2 suppress diffusion of the reducing agents Si and Mg from the base 1 into the electron-emissive layer 2 and also suppress flow of electric current because of high resistance of those layers.
  • Fig. 3B shows results of the analysis of the cathode containing Sc2O3 according to this embodiment.
  • the elements Si and Mg are dispersed uniformly in each of the base region and the electron-emissive region and such high peaks as shown in Fig. 3A are not observed.
  • the rare earth metal oxide prevents oxidation of the interfacial layer of the base 1 when the alkaline earth metal carbonate is decomposed to oxide or when dissociation reaction occurs in BaO or the like during the operation of the cathode.
  • Sc2O3 is contained in the electron-emissive layer 1, Sc2O3 reacts preferentially with BaCO3 or BaO according to the formulas (3), (5), (6) and (8) and accordingly there is not formed any oxide layer of NiO on the surface of the base 1.
  • the base 1 contains Si and Mg as reducing agents, layers of SiO2 and MgO are formed in the vicinity of the interface if Sc2O3 is not contained in the electron-emissive layer. Accordingly, diffusion of the reducing agents Si and Mg into the electron-emissive layer 2 is limited by the oxide layers of SiO2 and MgO and the reactions represented by the formulas (1) and (2) occur only in the vicinity of those oxide layers. As a result, oxide layers of SiO2 and MgO are formed preferentially in the vicinity of the interface particularly during the life test with the high current density and diffusion of Si and Mg into the electron-emissive layer is further limited, and thus the emission current under the normal condition is extremely lowered.
  • the rare earth metal oxide in the electron-emissive layer 2 suppress oxidation of Ni, Si and Mg to prevent formation of an oxide film in the interface region and in consequence the reducing elements Si and Mg easily diffuse deep into the electron-emissive layer 2. Accordingly, the reactions represented by the formulas (1) and (2) occur more homogeneously within the electron-emissive layer 2.
  • the rare earth metal oxide suitably controls diffusion rate of the reducing elements in the electron-emissive layer, the emission characteristics of the cathode can be maintained stably and in good condition even after the life test with the high current density for a long period.
  • a cathode containing a rare earth metal oxide of less than 0.1 wt.% can not achieve satisfactorily the effect of suppressing formation of the oxide layers of SiO2 and MgO in the vicinity of the interface and as a result the emission characteristics can not be improved sufficiently.
  • a rare earth metal oxide of more than 20 wt.% suppresses excessively diffusion of the reducing elements in the electron-emissive layer 2 and the emission characteristics can not be improved sufficiently either.
  • rare earth metal oxides containing La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, etc. are used.
  • Such oxides as Sc2O3, Y2O3 and Ce2O3 are particularly preferred.
  • 0.1 to 20 wt.% rare earth metal oxide powder is subjected to a heat treatment in a reducing atmosphere before it is mixed with an alkaline earth metal oxide.
  • This heat treatment may be perfomed in a gas containing hydrogen at a temperature of 800 o C or more, preferably 1000 o C or more, for a period of 10 minutes or more.
  • This heat treatment causes partial reduction of the rare earth metal oxide thereby to enhance the reactive property of the rare earth metal oxide.
  • Fig. 4A shows, in the same manner as in Fig. 2A, the emission current after the life test with 2.05 A/cm2 with regard to cathodes according to this embodiment. The lowering of the emission current in Fig. 4A is suppressed a little further than that in Fig. 2A.
  • Fig. 4B shows, in the same manner as in Fig.
  • a rare earth metal oxide is contained in the electron-emissive layer in the form of a composite oxide of Ba3Sc4O9 or Ba3Y4O9.
  • Fig. 5A shows, in the same manner as in Fig. 2A, the emission current after the life test with 2.05 A/cm2 with regard to cathodes according to this embodiment.
  • Fig. 5B shows, in the same manner as in Fig. 2B, the emission current after the life test with various high current densities with regard to cathodes according to this embodiment.
  • the electron-emissive layer 2 contains not only a rare earth metal oxide of 0.1 to 20 wt.% but also powder of 10 wt.% or less comprising at least one of Ni and Co.
  • Ni and/or Co powder serves to provide a better conductivity for the electron-emissive layer 2 and to improve the adhesive property of this layer 2 to the base.
  • Table I indicates the emission current under the normal condition as to cathodes according to this embodiment after the life test of 6000 hrs using a high current density (2.6 A/cm2) 4 times as large as 0.66 A/cm2.
  • Table I Sample Content in electron-emissive layer (wt.%) Normalized emission-current after life test (%) Sc2O3 Ni 0 - - 32 1 0.05 0.1 38 2 0.1 0.1 60 3 0.5 0.1 70 4 5 0.1 83 5 10 0.1 85 6 20 0.1 61 7 25 0.1 40 8 5 0.05 78 9 5 1 85 10 5 5 5 87 11 5 10 65 12 5 13 45
  • sample 0 is a conventional cathode in which the electron-emissive layer comprises a ternary alkaline earth metal oxide of (Ba, Sr, Ca) 0.
  • Samples 1 through 12 contain Sc2O3 and Ni in addition to the ternary alkaline earth metal oxide.
  • Sc2O3 of 0.1 to 20 wt.% and Ni of less than 10 wt.% are preferred for improvement of the emission characteristics of the cathode.
  • Ni exceeds 10 wt.%, sintering occurs between the Ni powder and the alkaline earth metal oxide powder to cause unfavorable influence on the surface of the electron-emissive layer, resulting in deterioration of the electron emission characteristics.
  • an electron-emissive layer containing Co can also be used effectively.
  • the electron-emissive layer 2 contains not only scandium oxide of 0.1 to 20 wt.% but also a reducing metal of 1 wt.% or less.
  • Table II shows, in the same manner as Table I, the emission current after the life test with the high current density as to cathodes containing Fe as a reducing element.
  • the reducing element Fe assists the rare earth metal oxide in suppressing formation of oxide layers of SiO2 and MgO in the interfacial layer of the base 1.
  • the content of Fe is preferably 1 wt.% or less. If it exceeds 1 wt.%, the alkaline earth metal oxide is reduced excessively and Ba is produced in an excessive amount, causing the lifetime of the cathode to be decreased.
  • Fe was described as the reducing metal in this embodiment, such metals as Ti, Zr, Hf, V, Nb, Ta, Si Al, Cu, Zn, Cr, Mo and W may also be used.
  • any of the rare earth metal oxides containing La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er or Tm may be substituted.
  • the electron-emissive layer 2 contains as a major element an alkaline earth metal oxide containing at least Ba and also contains a rare earth metal of 0.05 to 15 wt.%.
  • Fig. 6A shows, in the same manner as in Fig. 2A, the emission current after the life test with the current density of 2.05 A/cm2 as to cathodes according to this embodiment. As can be seen from this figure, lowering of the emission current in the cathodes of this embodiment is much suppressed as compared with the conventional cathode.
  • Fig. 6B shows, in the same manner as in Fig. 2B, the emission current after the life tests of 6000 hrs with various high current densities as to cathodes according to this embodiment.
  • a rare earth metal of more than 0.05 wt.% contributes effectively to an improvement of the emission characteristics.
  • the content of the rare earth metal oxide in the electron-emissive layer 2 is preferably in the range from 0.1 to 15 wt.% and more preferably in the range from 0.2 to 7 wt.%.
  • the cathode containing Sc or Y was shown in this embodiment, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er or Tm may also be used.
  • Fig. 7 is an enlarged fragmentary sectional view schematically illustrating a cathode according to a still further embodiment of the present invention.
  • the electron-emissive layer 2 comprises a first layer 2a formed on the base 1 and a second layer 2b formed on the first layer 2a.
  • the first layer 2a contains not only alkaline earth metal oxide powder 21 but also rare earth metal oxide powder 22 of 0. 1 to 20 wt.% containing Sc.
  • the second layer 2b contains only alkaline earth metal oxide powder 21.
  • each of the first and second layers 2a and 2b is formed to be approximately 40 ⁇ m in thickness.
  • the cathode of this embodiment has a particularly stable initial electron-emission characteristic of 1 to 2 A/cm2 under the normal condition at the operation temperature of 700 to 800°C.
  • any of the rare earth metal oxides containing La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er or Tm may be substituted.
  • Fig. 8 shows a cathode according to a still further embodiment of the present invention.
  • a sintered Ni powder layer 4 is formed on the surface of the base 1, and the electron-emissive layer 2 containing not only an alkaline earth metal oxide but also a rare earth metal oxide of 0.1 to 20 wt.% is formed on the sintered powder layer 4.
  • the sintered Ni powder layer is formed in the following manner. Ni metal powder having a grain size of 3 to 5 ⁇ m is mixed with nitrocellulose lacquer and butyl acetate so that a suspension is prepared. This suspension is applied to the base 1 by a spray method so that the applied suspension has a thickness of approximately 30 ⁇ m. Then, the applied suspension is subjected to a heat treatment in an atmosphere of hydrogen at 1000°C for 10 minutes so that it is sintered.
  • the sintered Ni powder layer 4 is porous and thus a part of the electron-emissive layer 2 applied thereon penetrates the sintered layer 4 to be in direct contact with the base 1. Even if the above described intermediate layer of SiO2, MgO or the like is formed in the region of contact with the base 1, lowering of the conductivity due to the formation of the intermediate layer can be prevented because a considerably large part of the electron-emissive layer 2 contacts the sintered layer 4.
  • the thickness of the sintered Ni powder layer 4 is chosen as 10 to 50 ⁇ m.
  • a sintered layer of less than 10 ⁇ m is not effective because the intermediate layer of oxide might be formed on the side of the electron-emissive layer, exceeding the sintered layer.
  • the thickness exceeds 50 ⁇ m, the alkaline earth metal oxide can not be sufficiently penetrated into the sintered layer 4 and thus does not sufficiently come in contact with the base 1 containing the reducing element and, as a result, activation of the electron-emissive layer 2 can not be made in a satisfactory manner.
  • Fig. 9 shows a cathode according to a still further embodiment of the present invention.
  • a rare earth metal oxide layer 5a or a rare earth metal layer 5b is provided between the base 1 and the electron-emissive layer 2 made of an alkaline earth metal oxide.
  • the rare earth metal oxide layer 5a or the rare earth metal layer 5b is formed by an electron beam evaporation method or a sputtering method prior to formation of the electron-emissive layer 2.
  • the rare earth metal dissolves from the layer 5a or 5b into the base 1. Accordingly, even if oxygen produced by dissociation of BaO or other similar phenomenon is diffused into the base 1, segregation of SiO2 and MgO in the interfacial region of the base 1 is suppressed because the rare earth metal dissolved in the base 1 reacts with the oxygen to form a rare earth metal oxide.
  • the rare earth metal dissolved into the base 1 serves to strengthen the adhesion between the layer 5a or 5b and the base 1 and to prevent embrittlement of the base 1 containing Ni as a major element.
  • Fig. 10 shows the emission current after the life test of 6000 hr with the current density of 2.05 A/cm2 with regard to cathodes provided with the rare earth metal oxide layer 5a of Sc2O3 or Y2O3 having various values of thickness.
  • the cathode having the rare earth metal oxide layer of less than 10 ⁇ m in thickness shows an extremely excellent characteristic in prevention of lowering of the emission current as compared with a conventional cathode.
  • the thickness of the rare earth metal oxide layer exceeds 10 ⁇ m, the reducing elements Si and Mg can not be diffused sufficiently from the base 1 into the electron-emissive layer 2 and separation of the rare earth metal oxide layer 5a from the base 1 may occur during the life test with the high current density.
  • Fig. 11 shows, in the same manner as Fig. 10, the emission current with regard to cathodes provided with the rare earth metal layer 5b containing Sa or Y having various values of thickness.
  • the cathode having the rare earth metal layer of less than 6 ⁇ m shows much less deterioration in the emission current as compared with a conventional cathode.
  • the thickness of the rare earth metal layer exceeds 6 ⁇ m, the reducing elements Si and Mg can not be diffused sufficiently from the base 1 into the electron-emissive layer 2, causing the emission current to be considerably decreased.
  • oxide layer 5a or the metal layer 5b containing Sc or Y was described in the embodiment in Fig. 9, an oxide or a metal containing at least one of the metals La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er and Tm may also be used.
  • a rare earth metal of 0.01 to 0.5 wt.% is contained in the base 1.
  • An electron-emissive layer 2 made of an alkaline earth metal oxide containing at least Ba is formed directly on this base 1.
  • Fig. 12 shows the relation between the rare earth metal content of Sc and/or Y in the base of the cathode according to this embodiment and the emission current after the life test of 6000 hrs with the current density of 2.05 A/cm2.
  • the cathode having the base 1 containing rare earth metal of 0.01 to 0.5 wt.% shows a by far smaller degree of lowering of the emission current compared with a conventional cathode. If the rare earth metal concentration is less than 0.01 wt.%, it can not serve to sufficiently suppress formation of oxide layers of SiO2 and MgO in the interfacial layer of the base 1.

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EP86305560A 1985-07-19 1986-07-18 Cathode for electron tube Expired - Lifetime EP0210805B1 (en)

Applications Claiming Priority (24)

Application Number Priority Date Filing Date Title
JP60160851A JPS6222347A (ja) 1985-07-19 1985-07-19 電子管用陰極
JP160851/85 1985-07-19
JP60229302A JPS6288240A (ja) 1985-10-14 1985-10-14 電子管用陰極
JP22930385A JPH0626096B2 (ja) 1985-10-14 1985-10-14 電子菅用陰極
JP229304/85 1985-10-14
JP229303/85 1985-10-14
JP229302/85 1985-10-14
JP60229304A JPS6288239A (ja) 1985-10-14 1985-10-14 電子管用陰極
JP231905/85 1985-10-15
JP60231906A JPS6290821A (ja) 1985-10-15 1985-10-15 電子管用陰極
JP23190585A JPH0743995B2 (ja) 1985-10-15 1985-10-15 電子管用陰極
JP23190485A JPH0782804B2 (ja) 1985-10-15 1985-10-15 電子管用陰極
JP231904/85 1985-10-15
JP231906/85 1985-10-15
JP61008365A JPS62165832A (ja) 1986-01-18 1986-01-18 電子管用陰極
JP61008366A JPS62165833A (ja) 1986-01-18 1986-01-18 電子管用陰極
JP8365/86 1986-01-18
JP8366/86 1986-01-18
JP61035670A JPS62193031A (ja) 1986-02-19 1986-02-19 電子管陰極
JP35670/86 1986-02-19
JP35671/86 1986-02-19
JP61035671A JPS62193032A (ja) 1986-02-19 1986-02-19 電子管陰極
JP41050/86 1986-02-25
JP4105086A JPH0782800B2 (ja) 1986-02-25 1986-02-25 電子管陰極

Publications (3)

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EP0210805A2 EP0210805A2 (en) 1987-02-04
EP0210805A3 EP0210805A3 (en) 1988-03-16
EP0210805B1 true EP0210805B1 (en) 1993-10-06

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EP86305560A Expired - Lifetime EP0210805B1 (en) 1985-07-19 1986-07-18 Cathode for electron tube

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US (1) US4797593A (zh)
EP (1) EP0210805B1 (zh)
CN (1) CN1004452B (zh)
CA (1) CA1270890A (zh)
DE (1) DE3689134T2 (zh)

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DE3689134T2 (de) 1994-03-03
DE3689134D1 (de) 1993-11-11
CN1004452B (zh) 1989-06-07
CA1270890A (en) 1990-06-26
EP0210805A3 (en) 1988-03-16
US4797593A (en) 1989-01-10
EP0210805A2 (en) 1987-02-04
CN86104753A (zh) 1987-01-14

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